Tires containing a monitoring device for monitoring an engineering condition therein

ABSTRACT

A method for monitoring various physical conditions of pneumatic tires, and to a tire including a monitoring device. More particularly, the invention relates to a method of monitoring tires which uses an active, self-powered programable electronic device which is installed in or on the interior surface of a pneumatic tire or on a tire rim. This device can be used for monitoring, storing and telemetering information such as temperature, pressure, tire rotations and/or other operating conditions of a pneumatic tire, along with tire identification information. The device can be activated by externally transmitted radio frequency waves and in response, the device compares or transmits information and provides a warning in the event a preselected limit is exceeded.

This application is a divisional of application Ser. No. 08/253,885,filed Jun. 3, 1994, now U.S. Pat. No. 5,500,065.

FIELD OF THE INVENTION

This invention pertains to a method for monitoring various conditions ofpneumatic tires and to tires containing a monitoring device. Moreparticularly, the invention relates to a method of monitoring tireswhich uses an active, self-powered, programable electronic device whichis generally installed in or on the interior portion of a pneumatic tireor on a tire rim. The device can be used for monitoring, storing andtelemetering information such as temperature, pressure, tire mileageand/or other operating conditions of a pneumatic tire, along with tireidentification information.

BACKGROUND OF THE INVENTION

It is desirable to monitor the condition of tires as to wear, internaltemperature and internal pressure. It is particularly advantageous tomonitor large truck tires since these are expensive and must beregularly maintained to maximize vehicle efficiency.

In the past, such monitoring activities have generally used a passiveintegrated circuit embedded within the body of the tire and activated bya radio frequency transmission which energizes the circuit by inductivemagnetic coupling. Passive devices which rely on inductive magneticcoupling or capacitive coupling generally have the disadvantage ofrequiring lengthy coil windings, thus requiring major modifications inthe tire construction and assembly process. Another serious disadvantagewith such passive devices is that the interrogator must be positioned invery close proximity to the tire, usually within a few inches of thetire, in order to allow communication between the tire and the device.Because of the proximity requirements, continuous monitoring isimpractical since it would require that an interrogator be mounted ateach wheel of the vehicle. Manual acquisition of data from the passivedevices embedded in each of the tires of a parked vehicle is alsocumbersome and time consuming because of the proximity requirements.

Other prior art devices used for monitoring tire conditions havecomprised self-powered circuits which are positioned external of thetire, such as at the valve stem. Externally mounted devices have thedisadvantage of being exposed to damage, such as from weather andvandalism. Another disadvantage with installing devices external of thetire is that the device itself introduces additional sealed joints fromwhich air may leak. Additionally, externally installed devices caneasily become disassociated from a particular tire which is beingmonitored.

Another disadvantage with known tire monitoring and identificationdevices is that communication transmissions are achieved usingconventional radio frequencies which generally require a relativelylarge antenna which must be mounted externally or secured to the tire insuch a manner which requires relatively major modifications in the tireconstruction or assembly process.

SUMMARY OF THE INVENTION

In accordance with an aspect of the present invention, a method ofmonitoring tires is provided in which an activatable monitoring deviceor tag is mounted within at least one tire of a vehicle, on the interiorsurface thereof, or on the tire rim. The device is activated by means ofan interrogator signal having a frequency in the microwave range. Inresponse to the signal, the monitoring device measures and transmitsinformation relating to one or more conditions such as the internalpressure and temperature of the tire, the number of rotations of thetire, and tire identification information. Desirably, the tireinformation is received at a monitoring station where the informationcan be viewed on a color coded, visual display, and even have an audiosignal and/or flashing lights to indicate an undesirable condition withrespect to acceptable values. The display can show all the tires of avehicle sequentially or at the same time. Alternatively, the monitoringdevice can be activated to transmit the various conditions to a hoststorage device located in a weigh station, a trucking terminal, etc.,which thus can record and contain the history of the transmittedcondition values of the individual tires.

The monitoring device includes an active circuit which is powered by adedicated, long life, miniature battery and one or more sensors fordetecting and transducing operating conditions. The device furtherincludes integrated circuitry; a programmable microprocessor forprocessing the electrical signals from the sensor and for data storageincluding tire identification information; and a microwavereceiver/transmitter for receiving and telemetering the processedelectrical signals from the sensors in response to an electromagneticsignal from an external interrogator. By using microwave frequencytransmissions, it is possible to achieve relatively long-rangetransmissions using a relatively small antenna. The monitoring devicecan be installed either on new tires during the manufacturing process oradded to existing tires.

The monitoring device is preferably capable of being programmed toremain in a dormant mode unless a condition limit has been exceeded suchthat the monitoring device does not respond to routine interrogationunless a condition limit has been exceeded.

The monitoring device can be secured to the tire wall by means of apocket or cover which holds the device to the tire. The cover or pocketcan be secured to the tire by utilizing a chemical or heat activatableadhesive. The monitoring device is secured to the tire in such a mannerand location as to minimize stress, strain, cyclic fatigue, impact andvibration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial cross-sectional view of a pneumatic tire inaccordance with the invention with monitoring devices installed at twoalternative locations within the pressurizable cavity of the pneumatictire;

FIG. 2 is a block diagram of the electrical components and antenna ofthe monitoring device utilized with the present invention:

FIG. 3 is a side elevation view of an alternate configuration of theelectrical components and antenna of the monitoring device shown in FIG.2;

FIG. 4 is a block diagram of the micro-chip contained in the monitoringdevice shown in FIG. 2;

FIG. 5 is a block diagram of an interrogator which communicates with andretrieves information from the monitoring device;

FIG. 6 is a cross-sectional view of an encapsulated electronicmonitoring device assembly;

FIG. 7 is a cross-sectional view of a monitoring device assembly whichis mounted to the interior wall of a pneumatic tire by means of a coversecured to the interior wall of the pneumatic tire;

FIG. 8 is a cross-sectional view of a monitoring device assembly whichis positioned within a recess on and is mounted to an interior wall of apneumatic tire by means of a cover secured to the interior wall of thepneumatic tire;

FIG. 9 is a perspective view of the cover securing the monitoring deviceassembly to the interior wall of the housing;

FIG. 10 is a cross-sectional view of a suitable cover formed on theinterior wall of a pneumatic tire for securing a monitoring devicethereto;

FIG. 11 is a sectional view of a pocket assembly in accordance withanother embodiment of the invention;

FIG. 12 is a top view of the pocket assembly of FIG. 11;

FIG. 13 is a sectional view of a tire having a monitoring deviceassembly embedded in the interior of the tire in the vicinity of thetire crown;

FIG. 14 is a sectional view of a tire having a monitoring deviceassembly embedded in the tire on the tire interior in the vicinity ofthe tire bead; and

FIG. 15 is a sectional view of another embodiment of the tire showingthe monitoring device assembly attached to the interior of the tire inthe vicinity of the tire crown.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In accordance with an embodiment of the invention, a method ofmonitoring at least one condition of a tire is provided including thesteps of providing the tire with an internally mounted monitoringdevice; sensing and measuring engineering conditions, including but notlimited to temperature, pressure, distance, speed, etc. and/or storingthe sensed conditions as data with the device pertaining to themonitored condition; activating the device to cause transmission of themeasured data; and optionally comparing the data to preselected limitsand signaling an alert if the limit is exceeded. The phrase "internallymounted" means that the monitoring device is built into the tire ormounted on an interior surface of a pressurizable cavity formed betweenthe tire and the rim of a tire/rim combination or on the tire rimitself. The monitoring device is desirably activated by the transmissionof a radio frequency interrogation signal when the tire is within adesired range of a signal transmitter. The monitored conditions caninclude pressure, temperature, or revolution and/or mileage information,and also tire history or identification information such as serialnumber, tire size, date and location of manufacture, retread informationand the like.

In accordance with another embodiment of the invention, a tire isprovided which is preferably a pneumatic tire having a monitoring deviceinternally mounted within the tire at a location as noted in the aboveparagraph. Regardless of the monitoring device location, it optionallycan be encased with materials set forth hereinbelow. When located in arecess or on the surface of the tire interior, it can optionally behoused within a cover or a pocket. The specific attachment or adheringmeans can be through the use of a chemical cure adhesive including aroom temperature amine curable adhesive or a heat activatable cureadhesive.

Referring now to the drawings, in FIG. 1 there is shown a partialsectional view of a pneumatic tire 5 having a monitoring device 10 or10' secured to the inner wall of the pneumatic tire 5 at two preferredlocations thereof. In practice, a pneumatic tire would generally haveonly one electronic monitoring device at any interior tire location oron tire rim 12. As apparent from FIG. 1, one preferred location is inthe vicinity of the tire bead below the end of the body ply turn-upwhere the sidewall bending stiffness is greatest and where the rollingtire stresses are at a minimum. The lower most extent of the tire beadlocation wherein such properties are obtained is generally the bottom ofthe tire bead. In a specific tire, for example, a 285/75R24.5 R299Truck/Bus Radial ("TBR"), this preferred location is a distance of aboutone to about two inches above the toe bottom of the tire. Above thenoted range, the cyclic strain amplitudes grow very quickly. As alsoshown in FIG. 1, another preferred location of the monitoring device ison the inside of the tire at the center of the tread crown where tirestresses from mounting and dismounting are at a minimum.

The monitoring device 10 is comprised of a microchip 20, an antenna 30,an amplifier 42, a battery 44, a pressure sensor 46, and optionaltemperature and mileage/distance sensors (not shown), populating acircuit board 48 as depicted in FIG. 2. While not shown in theembodiment of FIG. 2, it is envisioned that the microchip 20 itself cancontain all or some of the aforementioned components.

While optional, it is desirable that the monitoring device be containedin a rigid or semi-rigid encasement to enhance rigidity and inhibitstraining of the device. This reinforcing encasement or encapsulation isa solid material, i.e., non-foam compounds, which is compatible with thetire rubber, such as various urethanes, epoxies, unsaturatedpolyester-styrene resins, and hard rubber compositions. Hard rubbercompositions generally refer to any type of rubber or elastomer which iscrosslinked and has a Shore A hardness of from about 50 to about 100,and desirably a Shore D hardness of from about 5 to about 80 andpreferably a Shore D hardness from about 40 to about 80. We have foundthat the solid materials most suitable for use as reinforcementencasement or encapsulation of the device typically have an elasticmodulus (Young's Modulus, E) in the range of about 100 ksi (100,000pounds per square inch) to about 500 (500,000 pounds per square inch)ksi. The actual selected elastic modulus of the solid reinforcementencasement materials used to encase the device are a function of thestiffness of the monitoring device itself.

An example of the monitoring device being encapsulated is shown in FIG.6, wherein monitoring device 10 is encased within encasement orencapsulating material 16 to form monitoring device assembly 17. Asshown in FIG. 6, it is an important aspect of the present invention thatthe sensor 46, which measures pressure, have an opening, aperture, etc.,18 to allow an air path to the sensor so it can measure the internaltire pressure.

Referring now to FIGS. 7 and 8, and as noted above, monitoring deviceassembly 17 can optionally have a flexible housing such as pocket 75 orcover 80. Suitable housing materials which function to hold themonitoring device to the tire include generally flexible and resilientrubbers such as natural rubber or rubbers made from conjugated dieneshaving from 4 to 10 carbon atoms such as synthetic polyisoprene,polybutadiene, styrene-butadiene rubber, and the like, flexiblepolyurethanes, flexible epoxides, and the like, and having a hardness onthe Shore A hardness scale of from about 50 to about 95, and preferablyfrom about 55 to about 75.

FIG. 9 is a perspective view of FIGS. 7 and 8 showing the cover 80secured to the interior wall 7 of tire 5. The cover 80 has an adheringsurface which secures the monitoring device assembly to a surface of thetire, preferably within the pressurizable tire cavity. Slit 84 providesan air passage so that the pressure sensor can appropriately monitor airpressure.

FIG. 7 shows monitoring device assembly 17 secured to tire 5 throughcover 80. The cover has a slit 84 to allow a pressure sensor of thedevice to detect the internal tire pressure. Generally, cover 80 issecured to the interior portion of the tire. Except for the opening orslit 84 necessary for pressure sensing, the cover 80 surrounds themonitoring device assembly 17 as shown in FIG. 7, and is secured to theinterior portion of the tire about the perimeter of the monitoringdevice assembly.

As apparent from FIG. 8, the monitoring device assembly 17 is locatedwithin tire pocket or recess 75. The tire pocket or recess 75 can bemade by inserting a rectangular TEFLON® (PTFE) billet of the appropriatedimensions onto the uncured tire interliner at the location of thedesired recess 75. During tire manufacturing, the curing pressure of themold will press the billet into the tire inner liner and cure in therecess pocket 75 as shown in FIG. 8. Cover 80 is then attached about theperimeter of the monitoring device assembly to the tire inner liner.Cover 80 also has a slit 84 therein to allow detection of air pressure.Cover 80 may be co-cured with the green tire or may be attached to thetire after curing by use of various types of adhesives as discussedbelow.

Referring now to FIG. 10, when a cover 80 such as shown in theconfigurations of FIGS. 7 and 8 is utilized, a non-adhering sheet 86,constructed, for example from TEFLON® (PTFE) or silicon releasematerials, can be placed between the cover 80 and the underlying tireinner wall 7 to ensure that a cavity is formed to house the monitoringdevice assembly. The cover is then adhered to the interior of the tireutilizing a suitable adhesive system. After curing of the adhesivesystem, the non-adhering sheet 86 is removed. The monitoring device,whether or not encapsulated, can then be inserted through the slot offlexible cover 80. Alternatively, the monitoring device, whether or notencapsulated, can be positioned in an abutting relationship with tire 5and cover 80 installed thereover and adhered to tire 5 at the coverperimeter by a suitable adhesive.

In preferred embodiments as shown in FIGS. 11 and 12, the monitoringdevice is contained within housing pocket 90 which has a slot formounting the assembly within the pocket and through which the antenna ofthe monitoring device can project after assembly. Further, pocket 90includes an optional substrate 110 such as to assure adhesion of pocket90 to tire 5. The housing pocket 90 comprises a top portion or cap 92having a pocket cavity 94 for receiving and retaining monitoring deviceassembly through opening 96. Pocket cavity 94 is generally of a suitablesize and shape to snugly hold or secure monitoring device assembly.Pocket 90 also includes band 98 for securing and biasing antenna 30 ofthe monitoring device assembly to raised portion 102 of pocket 90.

Another manner of securing the monitoring device assembly 17 to tire 5is to physically embed monitoring device assembly 17 within tire 5during the manufacture of the tire by placing the device between thetie-gum ply 199 and inner liner ply 200 of the uncured tire. Aftercuring, the device is permanently contained in the tire structure. FIG.13 illustrates a tire cross section containing an embedded monitoringdevice assembly 17 positioned in the inner liner body ply portion 200located at or in the vicinity of tire crown 202 by this method. Crown202 is one of the preferred locations for placement of the monitoringdevice. Experience has shown that the monitoring device should notcontact the body ply 204 because such contact may degrade the durabilityand structural performance of body ply 204. Another preferred locationis near tire bead 210 as shown in FIG. 14. A small removable dowel 206is contained in the monitoring device assembly 17 at the time ofplacement in the green tire. The dowel 206 presses through inner linerply portion 200 upon the application of curing pressures to form a holeor aperture for air passage to the pressure sensor in the monitorassembly 17. The dowel 206 should have suitable dimensions and a smooth,rounded end to ensure passage through the soft inner liner rubberwithout damaging the mold bladder (not shown) which is used during thetire curing operation. If desired, the mold bladder can be reinforced atthe location of monitoring device assembly 17 and dowel 206. Dowel 206is removed after curing of the tire, leaving a finished air hole.

A second embodiment for embedding the monitoring device assembly isillustrated in FIG. 15. In this method, a dowel 220 is first insertedthrough an inner liner patch 222, and then into the monitoring deviceassembly 17. Next, monitoring device assembly 17 is sandwiched betweenthe uncured tire inner liner ply 200 and inner liner patch 222. Aftercuring, the monitoring device assembly 17 is permanently embeddedbetween patch 222 and ply 200. In this procedure, a larger, contoureddowel head 224 can be employed to further reduce trauma to the moldbladder (not shown).

The various adhesive systems which can be used to adhere the monitoringdevice to the tire embrace numerous chemical cure adhesives includingambient temperature amine curable adhesives. Heat cure adhesives canalso be used. Suitable chemical cure adhesives include conventionalsulfur cure systems such as various self vulcanizing cements, variouschemical vulcanizing fluids, and the like such as those sold by ThePatch Rubber Company of Roanoke Rapids, N.C.

The room temperature or ambient amine curable adhesive system comprisesinitially applying a treating agent to the various surfaces to beadhered (e.g., tire, cover, etc.) followed by the application of variousamine curable polymers or prepolymers. Suitable treating agents includevarious N-haloamides, the various N-halohydantoins, the variousN-haloimides, and combinations thereof. Examples of various desirableN-halohydantoins include 1,3-dichloro-5,5-dimethyl hydantoin;1,3-dibromo-5,5-dimethyl hydantoin;1,3-dichloro-5-methyl-5-isobutylhydantoin; and1,3-dichloro-5-methyl-5-hexyl hydantoin. Examples of N-haloamidesinclude N-bromoacetamide and tetrachloroglycoluril. Examples ofN-haloimides include N-bromosuccinimide and the various chlorosubstituted s-triazinetriones, commonly known as mono-, di-, andtrichloroisocyanuric acid. A preferred treating composition for use inthe practice of the present invention are the various mono-, di-, ortri-chloroisocyanuric acids, or combinations thereof.Trichloroisocyanuric acid is especially preferred.

The treating agents usually exist in solid form. They are readilysoluble in solvents such as acetone and the like and thus can be appliedin liquid form. Application of the treating agent generally occurs atambient temperatures. Application can occur through any conventionalmanner as through brushing, spraying, and the like. The amount appliedis such that the substrate is coated. Preferably, two or more coats ofthe treating agent or adhesive compound are used to ensure that all thecured rubber substrate surface has been coated.

Said ambient temperature amine curable adhesive systems are known to theart and literature as set forth in U.S. Pat. Nos. 4,718,469, 4,765,852,and 4,923,543, which are hereby fully incorporated by reference.

The heat cured adhesion systems generally utilize various adhesiveswhich upon heating to temperatures of at least 100° C. and generallyfrom about 115° to about 170° C. form an adhesive bond between the tiresubstrate and directly or indirectly with the monitoring device, itbeing understood that the curing time required is dependent ontemperature, with shorter times required at higher temperatures.Suitable conventional heat cured adhesives are known to the art andinclude various extruder cements, various retread and vulcanizingcements, and the like, for example, those sold by The Patch RubberCompany of Roanoke Rapids, N.C.

The adhesive may be directly applied to the monitoring device, to theencased or encapsulated monitoring device assembly, to the cover orpocket for the monitoring device, or any combination thereof.Alternatively, the monitoring device or monitoring device assembly canbe attached to the tire rim with a suitable adhesive. When a cover orpocket is utilized, an intermediate layer such as a cushion gum layer isoptionally but desirably contained between the adhesive applied to thecover or pocket on one hand and the adhesive applied to the tireinterior on the other hand to insure better adhesion of a monitoringdevice to the tire. Desirably, both the-tire and the cover or pockethave previously been buffed and cleaned with a solvent and coated withan adhesive.

Referring now to the monitoring device or tag 10, it includes a boardmade of a suitable material to hold the various components, one of whichis an integrated circuit or micro chip 20 as is shown in the blockdiagram of FIG. 4. The integrated circuit preferably includes one ormore analog to digital converters for digitally coding internal and orexternal analog signals. Suitable integrated circuits for use with theinvention are commercially available and/or can be fabricated. One suchcommercially available circuit 20 which has been found to beparticularly well suited for use with the invention is an RFID "Micron"chip available from Micron Communications, Inc. of Boise, Id. FIG. 4 isa block diagram of the "Micron" chip which is suitable for use with theinvention.

The chip 20 contains a central processing unit for processing commands,a 256 byte random access memory and micro wave radio circuitry fortransmission and reception of data. The center frequency of transmissionis 2.45 GHz. Circuitry for low and high frequency transmission bands areutilized by the chip to wake up or turn off to outside transmissions(instructions), according to a scheme developed by Micron and defined intheir protocol publication of Jul. 22, 1993, pre-release Ver. 0.95.Internal sensors for monitoring temperature, supply voltage, magneticfield strength and ambient light intensity are contained in the chip.The chip also has communication ports supporting digital and analoginput/output functions. The analog port can be programmed to source upto 2 milliamps of current. Analog input voltages from 0 to 2.5 volts canbe read for monitoring external sensors. Up to 256 analog ports can besampled by multiplexing. The chip can execute up to 30 predefinedcommands sent by radio transmission. These commands include functionsdealing with tag identification, memory read/writes, I/O portread/writes, alarm threshold settings, password/security andenable/disable commands.

The integrated circuit 20 also preferably includes the already discussedinternal sensors and/or one or more external analog ports for receivingan analog signal from one or more external sensors. The deviceoptionally but preferably includes a pressure transducer which ispreferably a solid state device such as a piezo-resistive pressuresensor. Suitable piezo-resistive pressure sensors are available fromLucas NovaSensor. Particularly preferred are Lucas NovaSensor's NPC-103series sensors.

The temperature sensor can also generally be any conventional sensorsuch as Model No. LM 35 CAZ made by National Semiconductor. The tiremileage detector can give out a readout signal in miles, kilometers,etc., and preferably may be in the form of a mild magnetic detectorresponsive to an external magnetic field which field is sensed by thedetector upon each full revolution of a tire. Alternatively, a detectormay detect each up or down cycle of the tire and produce a signal whichis counted. This counted number can then be sued to calculate tiremileage. An additional sensor which can be utilized is a speed sensorwhich monitors the speed of the vehicle.

The electronic monitoring device or tag 10 contains various componentsfor receiving and transferring information to the interrogator. Aspecific component is the amplifier 42 which is used to boost the analogsignal received from various sensors and transmit the same to the chipand subsequently to the interrogator. The amplifier can be connected toan external analog port of the microchip 20. The electronic monitoringdevice is active inasmuch as it contains a power source such as abattery and thus is self-powered. Any conventional long life alkalinebattery 44 can be utilized such as a 0.07 amp hour, lithium thionylchloride battery, type 7-10 made by Battery Engineering, Inc., of HydePark, Mass.

Monitor 10 also includes a microwave antenna 30 which can be locatedeither adjacent to the monitoring device shown in FIG. 2 oralternatively on the backside thereof as shown in FIG. 3. The antenna 30can be a suitable conducting means such as a single serpentine narrowwire or a thin sheet of a metal foil, for example, copper, so long as ithas a resonance frequency similar to the microwave transmissionfrequency. Generally, any microwave frequency can be utilized such asfrom about 1×10⁹ to about 5×10⁹ hertz with a suitable frequency beingfrom about 2.40 to about 2.49×10⁹ hertz.

Another embodiment, not shown, utilizes sensors exterior of monitoringdevice 10 as in the form of decals having lead lines running to themonitoring chip.

FIG. 5 is a block diagram of a generic type interrogator 60 which can beused to communicate with and retrieve digitally coded information fromthe electronic monitoring device. The interrogator includes microwavetransmitter and receive circuits for communicating with the micro chip.The RP transmitter utilizes dual frequency bands so that only tags (i.e.monitoring devices) programmed to respond to a certain band will beactivated, leaving the others dormant and conserving battery power. Thisis called "data band switching" and is defined as part of the publicdomain Micron protocol. The interrogator includes circuitry to receiveand transmit using spread spectrum modulation as defined in the Micronprotocol and as required by the FCC for microwave communication devices.The power level of transmission is user selectable and either one or twoantennas can be employed by the interrogator to improve reception. Theinterrogator includes I/O communications hardware to support interactionwith a host computer via parallel, serial RS-232, RS-485 and Ethernetlinks. A commercially manufactured interrogator of the type described isavailable from Unisys Corp., Salt Lake City, Utah. The interrogator canbe interfaced with a computer 70 to allow downloading, archiving, andanalysis of data transmitted from the electronic monitoring device 10.Moreover, different interrogators or a plurality thereof can be utilizedwith respect to different interrogation situations.

The interrogator can be remotely located in a vehicle, e.g., a truck, topermit intermittent monitoring at regular intervals such as every thirtyminutes, to alert the driver of the vehicle of any imminent or impendingproblems such as over or under inflation or abnormally hightemperatures. Alternatively, the interrogator can be located at avehicle service stop, e.g., fuel station, trucking terminal, or at anyother convenient location for archival, and/or current sensor readoutsof tire pressure and tire revolutions, etc., as through visual readouts,flashing lights, etc., as noted above. The monitoring devices in eachtire can be interrogated for information at regular or arbitraryintervals and the data can be stored on a computer interfaced to theinterrogator. The monitoring device 10 can also be programmed to act asan alarm system to warn of extreme temperature or pressure conditions,or it may be used to log pressure and/or temperature histories duringtire operation. Such data can be used, for example, to evaluate theretreadability of truck tires.

The interrogator includes various features such as software protocol forsorting, identifying and communicating with multiple monitoring deviceswithout ambiguity, thus enabling a signal interrogator to quickly sortand retrieve information from a plurality of monitoring devicesassociated with individual tires on a vehicle or on multiple vehicles.The broadcast range, from within a tire can vary, such as in excess offifty feet, thus permitting a stationary interrogator to quickly queryall tire chips on a vehicle which is passing by the interrogator or froman on board vehicle location.

In accordance with the preferred mode of the invention, a tire isprovided with a self-powered monitoring device on the interior or withinthe tire or on the tire material. The monitoring device includes meansto sense and store data regarding a tire condition, such as temperatureor pressure. In response to a triggering signal, the power source of themonitoring device is activated and the device transits the conditiondata. For example, the monitoring device may be identified by having theinterrogator read the identification code associated with the tire towhich the monitoring device is affixed. The identification code can, forexample, be stored as a 10 byte number, the first 4 bytes containing astandard international classification (SIC) code, the next 2 bytescontaining a specialty code, and the last 4 bytes identifying theparticular tire. Further in accordance with the preferred mode of theinvention, the monitoring devices 10 include low to high data bandswitching for selective communication between multiple interrogators andmultiple monitoring devices. The low band can correspond to a dormantmode wherein battery power is conserved. Monitoring device 10 willremain dormant unless an interrogator broadcasts a low band instructionto activate the device. The monitoring device and interrogatorfrequencies can be switched upon command. This allows for selectivegroups of monitoring devices to become active and respond to aninterrogator broadcast while others remain dormant. The monitoringdevice frequency can be switched by an externally measured event whichis being monitored by a sensing device (e.g. temperature) so that itactivates in response to an interrogator upon a preset limit to amonitored condition being exceeded. High and low sensor thresholds canbe programmed to determine when frequency switching occurs, thusenabling the monitoring devices to operate an alarm mode.

Also in accordance with a preferred mode of the invention,communications between multiple monitoring devices and an interrogatoror multiple interrogators is facilitated by means of an arbitrationmethod, thereby permitting unambiguous communications. The interrogator,monitoring device, and data communication protocol preferably allowvarious commands to be transmitted from the interrogator to themonitoring device. Examples of desired commands include functionsdealing with tire identification, memory, digital and analog portread/writes, alarm threshold settings, password and security data andenable and disable commands. These commands determine the functionalityof the monitoring device and permit customization of operation fordifferent applications. For example, through software commands amonitoring device can be set to ignore inquiries from an interrogatorunless a tire temperature exceeds a certain threshold or an air pressurefalls below a given set point. Alternatively, the monitoring devicecould be set to respond to an on board vehicle interrogator request forperiodic readings of temperature and pressure during tire operation inthe field. Battery life would dictate the frequency and duration ofcommunications that are possible.

While in accordance with the patent statutes the best mode and preferredembodiment has been set forth, the scope of the invention is not limitedthereto, but rather by the scope of the attached claims.

What is claimed is:
 1. A tire having means for monitoring at least oneengineering condition of the tire, comprising:the tire mounted on a rimdefining a pressurizable cavity between the tire and said rim; amonitoring device, said monitoring device in fluid communication withsaid pressurizable cavity and located on a boundary of saidpressurizable cavity so as to minimize stress, strain, cyclic fatigue,impact and vibration, said monitoring device including a battery, acircuit for data band switching, an integrated circuit including meansfor storing data, at least one sensor for sensing each engineeringcondition, means for converting each of said sensed conditions to datafor storing, means for energizing the circuit for data band switching toactivate the battery from a passive mode to an active mode, means fortransmitting said data responsive to a signal while the battery isactive, and means for energizing the circuit for data band switching todeactivate the battery from the active mode to the passive mode aftertransmitting said data.
 2. The tire having means for monitoring as setforth in claim 1, wherein said signal is a microwave frequency signal.3. The tire having means for monitoring as set forth in claim 2, furtherincluding an antenna for receiving the signal and for transmitting saiddata.
 4. The tire having means for monitoring as set forth in claim 1,wherein said monitoring device includes means for comparing the sensedengineering condition with a preselected limit and means fortransmitting the sensed engineering condition as a signal when thecondition exceeds said preselected limit.
 5. The tire having means formonitoring as set forth in claim 1, wherein said monitoring device islocated in a center portion of a tread crown below a body ply.
 6. Thetire having means for monitoring as set forth in claim 1, wherein saidmonitoring device is located in the vicinity of a tire bead below a bodyply.